The cathode-ray tube of the present invention includes a multicolor cathodoluminescent display screen, a plurality of electron beam sources, and is used in association with a scanning system that controllably directs the electron beams toward the display screen. The beams are projected through a multiapertured shadow mask positioned between the electron beam sources and the display screen. The beam paths through the mask are such that each beam impinges upon and excites only one type of color phosphor material in the screen.
The shadow mask is a very precisely constructed, very precisely positioned component of the cathode-ray tube. It consists of a membrane of electron beam absorbing material with a very closely patterned array of holes. These holes are required to be accurately aligned between the electron beam sources and specific groups of dots of phosphor on the display screen so as to permit passage only of the particular beam that is intended to address a designated phosphor dot. Any portion of the beam that would fall outside the dot area is intercepted and absorbed by the membrane material.
The mounting structure for the shadow mask of the contemplated cathode-ray tube includes a closed frame over which the membrane is stretched and securely fastened. The frame must be substantially rigid to avoid any buckling due to the tension of the membrane, and it must be securely mounted in the envelope of the cathode-ray tube in a manner that will resist distortion due to vibration.
Prior to the present invention, shadow mask frames typically have been formed by a continuous strip of rigid material with inwardly directed flanges along each edge. The flanges provided stiffening of the structure and one flange provided the surface to which the membrane was attached. Spring biased clips were welded to the outer side of the strip and were adapted to fasten in a precise manner to the envelope of the cathode-ray tube.
It is an objective of the present invention to maximize the display area of the display screen relative to the overall dimension of the tube. This is important in a number of applications, as for example where a number of cathode-ray tube displays are required in a restricted panel area, e.g., the instrument panel in the cockpit of an airplane. It will be understood that the display area of a cathode-ray tube incorporating the above-described prior shadow mask frame structure was restricted by the width of the flange to which the membrane was attached and by the location of the mounting clips between the frame and the envelope. Thus it is a specific objective of this invention to provide a rigid frame for the shadow mask membrane with reduced flange width. Still further, it is an objective of this invention to provide a mounting structure that does not require space between the frame and the cathode-ray tube envelope.